You want a medium telephoto lens for your Canon dSLR, something with a constant aperture, solidly built with pro quality, yet light enough to carry on adventure to some faraway part of the world. You have looked at the f2.8 models but didn't think you could afford them or the Sherpa to carry them. The Canon EF 70-200mm f4 IS USM L lens might be just what you're looking for. Its light weight, professional quality, along with its practical focal range make the lens ideal for travel, expeditions, and photojournalism. It has Canon's EF lens mount, making it compatible with all of Canon's digital SLRs, full-frame and APS-C, as well as all Canon EOS film SLRs. The version is the same size as its non-IS sibling, only slightly heavier; its price is about 45 percent lower than the IS version's approximately $1,100 price tag, though. Along with the 70-200mm f4 IS USM L, Canon offers other professional L-series lightweight zooms, including the 24-105mm f4 IS USM L, and the 17-40mm f4 USM L.

Design Part of Canon's L series of lenses, offering professional grade durability, with its signature putty-colored finish. Utilizes a ring-type USM (ultrasonic motor) for fast and quiet autofocusing. Has a maximum aperture of f4 through the entire zoom range, and a minimum aperture of f32. Circular aperture diaphragm for better blur characteristics when shooting at wider apertures. (The quality of rendering in shallow-depth-of-field is known as bokeh.) When mounted an APS-C sensor-sized dSLR, such as the EOS 50D or the EOS Rebel XSi, it has a 35mm-equivalent focal length of 112 to 320mm. Weighs 27.2 ounces, is 6.8 inches long and 3 inches in diameter. There is a distance scale window, with scales in both feet and meters. For those who like to shoot infrared, there are special infrared focusing marks (displayed in red) for focusing at 70mm and 100mm. These are necessary because infrared light focuses at a slightly different point than daylight. The lens is moisture and dust sealed, with an O-ring at the lens mount that creates an almost completely weather-proof seal when mounted on an EOS-1xxx series body.

Features Constructed with one fluorite lens element and two UD (ultralow dispersion) elements for maximum sharpness and clarity. Also, uses Canon's Super Spectra coatings to reduce ghosting and flare. Only lead-free glass is used in its manufacture. Canon's optical image-stabilization system, with up to four stops of correction. There are two IS modes, selectable via a switch on the lens barrel. Mode 1 corrects for movement along both the horizontal and vertical axes. Mode 2 turns off the horizontal correction to accommodate panning.  There is a two position focus-limiter switch. One sets the focus range from 1.2 meters (its closest focusing distance) to infinity and the other sets it from 3 meters to infinity. This is handy when you are shooting beyond 3 meters because this way the lens doesn't have to work so hard, and makes it less likely to accidentally focus on any objects in the immediate foreground. It comes well accessorized with a lens hood and a soft drawstring pouch.

Hands-on
Weighing just more than 27 ounces, its light weight makes it very comfortable to handhold, especially compared with Canon's almost twice as heavy f2.8 version. That, along with the IS, make a tripod or a monopod unnecessary in most cases. It doesn't come with a tripod collar like the f2.8 version, although you can buy one (#2889A002) for about $115. It feels easily maneuverable, focuses fast, and doesn't weigh you down, even after a long day of shooting. Although its 47.3-inch closest focusing distance precludes any macro work, you won't miss it. With its IS capable of up to four stops of correction, someone typically shooting at 1/250 second should theoretically be able to shoot handheld as slow as 1/15 second and still get a blur-free image. The IS automatically switches off when the camera is placed on a tripod.

About The Author

Matthew Fitzgerald, a CNET associate editor, has been involved with digital camera technology and the photo industry for more than 15 years. His background includes work as a professional photographer, a technical representative, and a repair technician.